Browsing by Author "Vanegas, Pablo"

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    A multiple criteria heuristic solution method for locating near to optimal contiguous and compact sites in raster maps
    (2011) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos
    A high performance heuristic solution method is proposed able to locate near to optimal sites composed by a given number of cells (raster structure). These sites must be compact and maximize levels of the sites intrinsic multiple criteria suitability. To validate the heuristic approach, a comparison with a mathematical formulation is performed with afforestation data of regions within the Netherlands, Denmark, and Flanders. This reveals that the heuristic is considerably faster than the mathematical method and the objective values obtained with the two approaches are substantially similar. A sensitivity analysis shows that the region's homogeneity plays an important role in the performance of the process identifying most favourable sites. Moreover, computation time follows a power model in the number of cells forming the site.
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    Budget constraint in reforestation meant for minimizing sediment load at a watershed outlet
    (2010-03-17) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos
    Policy and decision makers dealing with environmental conservation and land use planning often require identifying potential sites for contributing to minimize sediment flow reaching riverbeds. This could be one of the environmental objectives of reforestation initiatives. An Integer Programming (IP) formulation for selecting a predefined number of locations to minimize sediment load at a watershed outlet has been previously developed in [1]. This paper tests that formulation under the assumption that the area to be reforested is not known in advance, a budget constraint is included instead. Therefore the extension of the reforested area is subject to this budget constraint, which makes the problem more complex. Several experiments are performed for two watersheds in South Dakota in the USA. The results show the sediment load at the watershed outlet as well as the erosion levels, slopes and distances to the riverbeds of the locations selected to be reforested.
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    Compactness and flow minimization requirements in reforestation initiatives: An integer programming (IP) formulation
    (2009) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos
    Identifying optimal sites on raster maps is a complex problem when the sites are larger than the cell size. Optimal sites involves a trade-off between the intrinsic characteristics of individual cells and the spatial configuration of the cells. Although there are a number of techniques to solve the site allocation problem, those solutions do not consider spatial interactions between the cells forming the site. This paper presents an Integer Programming Formulation (IP) for allocating a predefined number of cells satisfying the following criteria: 1) minimize flow (water, sediment) reaching the outlet of a watershed, 2) maximize/minimize intrinsic characteristics of the cells, and 3) form a compact patch. Although the core structure of the IP formulation can be applied for different sorts of flow and intrinsic characteristics, it is targeted to a reforestation application. The proposed approach is applied to perform several experiments in two watersheds in South Dakota in the USA for searching a given number of best cells (1) minimizing sediment reaching the watershed outlet,(2) maximizing the environmental criteria, and (3) forming a compact patch. The results obtained with the IP formulation are in agreement with expert assessments of erosion levels, slopes and distances to the riverbeds.
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    Compactness in spatial decision support: A literature review
    (2010-03-23) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos
    The development of Spatial Decision Support Systems (SDSSs) which explicitly consider spatial relations has had a significant growth over recent years. The main intention of this paper is reviewing spatial optimization approaches for identifying contiguous and compact areas fulfilling particular criteria. These approaches explicitly consider topological spatial relations between geographical entities (cells, lines, points, areas). In this direction, spatial optimization techniques as heuristics, meta-heuristics, and mathematical programming are reviewed. Since the application fields, the nature of the approaches, the data format, and the size of the reviewed works are very diverse, high level comparison is made in order to identify critical issues regarding the identification of contiguous and compact areas in digital geographical information.
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    Integer Programming (IP) formulation for minimizing sediment delivery in a watershed by reforestation of optimal sites
    (2009-08-12) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos
    Several approaches exist to model the production, transport and delivery of water and sediment flows in watersheds but none of these are dealing with spatial optimality requirements. However, policy and decision makers dealing with environmental conservation and land use planning often require identifying potential sites for contributing to minimize sediment flow reaching riverbeds. This is the case of reforestation initiatives, which can have sediment flow minimization among their objectives. This paper proposes an Integer Programming (IP) formulation for selecting a predefined number of locations to minimize sediment load at a watershed outlet. Although the core structure of the IP model can be applied for different sorts of flow, the formulation is targeted to minimization of sediment delivery. Several experiments are performed for two watersheds in South Dakota in the USA. The results are in agreement with expert assessments of erosion levels, slopes and distances to the riverbeds, which in turn allows concluding that this approach is suitable for minimizing sediment flow.
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    Localización de sitios en mapas raster para minimizar impactos de flujo
    (Universidad de Cuenca, 2010-12) Vanegas, Pablo; Cattrysse, Dirk; Van Orshoven, Jos; Universidad de Cuenca; Dirección de Investigación de la Universidad de Cuenca; DIUC
    Policy and decision makers dealing with environmental conservation and land use planning often require identifying potential sites for contributing to minimize sediment flow reaching riverbeds. This is the case of reforestation initiatives, which can have sediment flow minimization among their objectives. This paper proposes an Integer Programming (IP) formulation and a Heuristic solution method for selecting a predefined number of locations to be reforested in order to minimize sediment load at a given outlet in a watershed. Although the core structure of both methods can be applied for different sorts of flow, the formulations are targeted to minimization of sediment delivery. The proposed approaches make use of a Single Flow Direction (SFD) raster map covering the watershed in order to construct a tree structure so that the outlet cell corresponds to the root node in the tree. The results obtained with both approaches are in agreement with expert assessments of erosion levels, slopes and distances to the riverbeds, which in turn allow concluding that the studied approaches are suitable for minimizing sediment flow.
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    Upgrading geographic information systems to spatial decision support systems
    (2011-04-17) Van Orshoven, Jos; Kint, Vincent; Wijffels, Anja; Estrella, René; Bencsik, Gergely; Vanegas, Pablo; Muys, Bart; Cattrysse, Dirk; Dondeyne, Stefaan
    A GIS is capable of identifying a set of land units meeting positional, temporal, topological and multiple on-site attribute criteria. Based on the combination of its generic analytical functionalities, a GIS can also be used to rank the alternative land units and propose the best or worst ones in terms of the non-weighted or weighted criteria. More advanced multi-criteria decision methods are however not easily incorporated in the GIS-framework so that extension with dedicated tools is required to upgrade the GIS to a full blown sDSS. In this paper we illustrate this upgrading of GIS to sDSS and we argue that when also temporal alternatives are dealt with, the DSS can be termed spatio-temporal. Three statements are made: (i) the presented rationale is challenged by phenomena of spatial and spatio-temporal interaction, (ii) important research avenues are present in order to optimize topological and off-site decision attributes in the spatial and spatio-temporal decision problems and (iii) the forestry domain is very suitable for study and application of all the mentioned issues due to the explicit spatial and temporal nature of the management issues which must be addressed.
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    Validación de un algoritmo robusto para la estimación del movimiento en secuencias de imágenes cardiacas
    (Universidad de Cuenca, 2015) Medina, Rubén; Ibarra, Emiro; Morocho, Villie; Vanegas, Pablo; Universidad de Cuenca; Dirección de Investigación de la Universidad de Cuenca; DIUC
    This paper describes the validation of a sparse based optical flow algorithm using two sequences extracted from the Sintel database and also images extracted from a tagged magnetic resonance image sequence representing a short–axis slice located at the mid-wall of the left ventricle. Results are promising as the average magnitude error for the Sintel sequences is lower than 3 pixels and lower than 1 mm for the tagged MRI.